Cam-controlled electrical switch consisting of axially aligned units



Nov. 10, 1959 H. NAIMER 2,912,527

, CAM-CONTROLLED ELECTRICAL SWITCH CONSISTING OF AXIALLY ALIGNED UNITS Filed April 19, 1957 Ill/III] venior Hwsser Nil/1E6 United States Patent CAM-CONTROLLED ELECTRICAL SWITCH CON- SISTING OF AXIALLY ALIGNED UNITS This invention relates to cam-controlled electrical switches of the type which comprises a plurality of camactuated switch units arranged along a common axis of rotation. The usual type of these switches comprises an operating shaft which carries and couples the cams and which consists of metal and has usually a polygonal profile. This construction, which is generally used, involves a number of disadvantages, the most important of which are:

In selecting the profile of the shaft, standardized rolled sections must be employed, usually square or hexagonal sections, in order to avoid an expensive special manufacture, in spite of the fact such sections are not very favourable'due to the play of the cams which results from the manufuacturing tolerances of the cam. Moreover, larger tolerances in the dimensions of said bar material must always be accepted, which is a disadvantage for the precise functioning of the switchgear.

For reasons of cost it is further necessary to use steel as material for the shaft so that an electroplating of the switch shaft is required for surface protection. In addition to the fact that it is not possible in mass production always to obtain a plating of the same thickness on all shafts, which gives rise to further variations in the final tolerances of the section bar, that surface protection is inadequate, even if it is very carefully made, if the switch is used in a room filled with a corrosive atmosphere, which is often inevitable.

The switch shafts must be cut to length in dependence on the overall length of the switch, i.e., on the number of units forming the switch. In addition to the manufacturingwork required for this operation, this involves the need for a large stock of shafts of standardized lengths. A reshaping of such stocks, as is often necessary in the case of difficulties in the supply of bar material, causes losses of time and particularly of material.

For electrical reasons a metal shaft must be sufliciently spaced from the live parts of the switch to ensure that the inevitable creep paths are sufliciently long. This requirement alone gives rise to dimensions of the switch which are larger than would be required for mechanical reasons. In addition, where a metal shaft is provided it must either be effectively insulated from the actuating member or must be perfectly grounded, which involves certain structural difiiculties.

In the desire to provide a construction which enablesa switch which consists of several axially aligned switch units to be assembled from the fewest number of identical parts, a cam-controlled electrical switch has been proposed which consists of axially aligned units and in which cams which actuate the circuit breaking members are provided with shaft stubs on both sides, at least one of which shaft stubs of each cam serves for rotatably supporting the cam in'a wall of a switch unit and each of which shaft stubs may also serve for coupling the cam to an axially adjacent 2,912,527 Patented Nov. 10, 1959 ice to be plugged into the bush of an axially adjacent cam to couple both cams for joint rotation. The present invention relates to an important development of this structure.

The attempt to build this switch shows that the costs involved in the manufacture of suitable cams is very high. If applied to the practically important case in which the switch consists of a larger number, e.g., of six or more units, and if it is considered that to ensure safe electrical contacts the rotation of such a switch requires considerable accumulating counterforces to be overcome in the switch unit, it will be seen that the turning member consisting of several cams plugged together must have a torsion strength which can be provided only by high-grade materials of construction, particularly by metal. Metal cams, however, are expensive die-castings, which do not afford an improvement over the construction described Whereas it is hereinbefore also for electrical reasons. known that metal parts such as cams, gear wheels and the like which are subjected to high stresses may be made of high-grade plastics, such as laminated thermosetting plastics based on phenol-formaldehyde and with a textile reinforcement, such plastics are also too expensive in the present connection and would require special measures at the journals because they are entirely unsuitable in view of the switch casings, which consist of similar plastics and in which said parts are to be rotatably supported. In this connection it is of special importance that such cams having widely varying external shapes but equal internal parts must lend themselves to manufacture by a method which is suitable for inexpensive mass production. All these difficulties have previously prevented the practical realization of the proposal mentioned hereinbefore.

This problem is solved by the invention in a switch of the type mentioned initially hereinbefore by making the cams of a high-melting, electrically insulating thermoplastic resin, which has a high mechanical strength and toughness and a moderate elasticity and high resistance to abrasion, all in a degree which is obtained, e.g., in plastics based on polyamides or superpolyamides. It is surpris ing that it would be possible to make cams which fulfill all the requirements from a thermoplastic resin, in view of the previous belief that these requirements are partly inconsistent with each other and that thermoplastic resins are usually not taken into consideration for the present purposes owing to inadequate strength and heat-resisting qualities. More particularly, it is surprising that according to the invention even a relatively long switch shaft can be built up from several cam elements without causing intolerable torsion to be set up within the shaft itself. It is also surprising that plastics of the type just described have excellent sliding qualities relative to the casing parts in which they are rotatably supported and which consist in most cases of thermosetting materials. This is of de cisive importance because the journals cannot be serviced throughout the life of the switch and the good sliding qualities must also be retained when the switch is exposed toa corrosive atmosphere.

To explain the invention, reference is made to the accompanying diagrammatic drawings, in which Fig. 1 is a longitudinal sectional view showing a cam-controlled switch which consists of three switch units and a stepping gear, whereas the jumper bridges and switch contacts, terminals, retaining springs and the like, which are of no interest in this connection, are omitted. Figs. 2 and 3 are an end view and a side view, partly in section, of a cam according to the invention. Fig. 4 shows the connection of the cam according to the invention with an operating handle and Fig. 5 is a side view of one of said cams, with the turning grip omitted. Fig. 6 shows that it is, possible to fulfil several switching requirements with one plastic cam according to the invention by providing cams selectively with control elevations or depressions disposed at different points.

In Fig. 1, numeral 1 denotes the casings of the switch un t 2 the ea .Qf th steppi e and 3 the thr e ams, efo e w c a s a e hap d s pp ng Whe 6 is arranged, which is also formed according to the invention. In ,Fig. 4, an operating handle is coupled by the jaws 5 in a manner which will be described hereinafter to the stepping wheel 6 belonging to the stepping gear. That stepping wheel is essentially a multiple cam. For this reason what Will be said hereinafter of the switch cams applies analogously also to that stepping wheel. The casings 1 form chambers which accommodate in known manner the jumper bridges and the associated c uati g m an co i g es; 9f a rol whi h engages the cam and a plunger which operates the jumper bridge. The last casing 1 is closed by acover 7. All asi 1, .2 a he c ve 7 ar he d together by axial y exten in cre or o e tain g means (n S w Eachcam, Figs. 2, 3, consistsof'the actual .cam disc 8, which is provided on both sides with shaft stubs 9, 10, which are preferably integral with the cam. The shaft stubs serve in known manner for rotatably mounting the cams in the casings 1 or in the cover 7; for this reason they have a cylindrical external shape whereas said casing parts form suitable bearings, e.g., in the form of flanges 11. In order to preclude excessive mechanical strain on the bearings, each cam 3 is rotatably supported in a casing 1 or 2 only on one side, as is shown in Fig. 1. As is distinctly shown in Fig. 2, the shaft stub 10 has ,a coupling extension 14, which takes here the form of a pin and has a suitable profile, e.g. a square profile, whereas the shaft stub 9 has a recessformed with aco nform ing profileof suflicient depth for fittingly receiving the pinshaped shaft stub 14 of the adjacent cam. Thus the cams are simply fitted one in the other, as is shown in Fig. 1 and are thus coupled for joint rotation. On the other hand, they are held without axial play in thecasing because they have no freedom of lateral movement therein.

The moderate elasticity of the plastic used hereensures in the case of an appropriate design that the cams can be plugged together practically without play. On the other hand, that elasticity surprisingly does vnot adversely affect a ad q y ec s t a m s on o the desi ed an of rotation. Even in switches which are eomposed of a very large number of individual switches, the tough ness of the plastic ensures an adequate resistance to fracture and permits also of a compensation of inevitable small manufacturing and assembling tolerances, which mayresult, e.g., in a slight misalignment of the journals. In conjunction with the favourable sliding properties of the plastics used here, this results in a sufliciently exact but reliably non-clamping bearing arrangement of the switch shaft consisting of the individual cams; this result is surprising for any of theknown plastics. 'The favourable behaviour regarding abrasion resistance and sliding properties is also important for the cooperation of the cam with the plunger which actuates the contact bridge.

The cam 6 forming the stepping wheel may have shaft stubs somewhat different from those of the switch cams. One of its shaft stubs 1-5 has an outwardly protruding extension 15a of non-cylindrical shape, in the present embodiment of hexagonal section. That extension is continued by a squarepin 16. The operating ,handlecontainsinknown manner jaws 5, which are pulled by means of ,a screw 19 into the tapering grip part 4 so that they are forced against the ,square 16. A ,sufiiciently firm coupling between the grip 4 and the cam 6 and thus with all other cams 3 is ensured by the extension 4a of the grip .4 makingconnection with the hexagonal portion 15.

. In the present example the stepping gear is disposed between .the first switch unit and the actuating member 4. It can be realized, however, that this arrangement is n esse ial beca selhm .Q the fi s switch uni 4: can easily be provided with an extension 15, 15a and a pin 16 though this would eliminate the desirable uniformity of the switch cams.

Fig. 6 shows a cam which consists of a serrated core 26 and a profiled cam ring 27, the contour of which is selected according to the s witehing requirements of each case. The cores 26 may be kept on stock.

T1 6 i llll l g portions should be given a tubular section with multiple teeth. An. example is also shown in Fig. 6, wherein part 26 is the coupling pin of the adjacent cam. This ensures an optimum transmission of forces with the least expenditure of material. tooth coupling profile enables each cam to be mounted relative to those of the adjacent switch chambers at an angle which is a multiple of the pitch angle of the teeth. This enables a considerable reduction in the number of cam profiles required for controlling the electrical contacts. The tubular section has also the advantage that a duct is formed which extends centrally throughout the switch and maybe-used for a number of .special functions desired in switch construction (e.g., double shaft, pushbutton actuation through the switch, etc.).

The semielastic properties of the superpolyamides enable the virtual elimination of the radial play which is otherwise required. This ensures that even in switches having a large number of units the transmission of torsion corresponds to that of a steel shaft. Because the cam as such is injection-moulded, the timeof manufacture 'is in no way prolonged by the simultaneous injectionmoulding of the coupling profile on both sides. This applies also to the stepping wheel. Thus notime is required for the manufacture of the shaft. A finished switch can easily be extended or reduced by some switch chambers without requiring a replacement of the shaft, as was necessary before. Difierent switch types (for different current values) can easily be coupled by an adapter whereas previously special, now standardized, switch shafts were required for this purpose. From the electrical aspect difficulties due to creep paths are eliminated and absolute shockproofness for the operator is ensured without special design measures. In operation there is absolute safety against destructing influences by the humidity of the air, marine air (saltcontent) or other corrosive atmospheres. one or several switchchambers can be replacedon the pot WilhQl d a s m y of t ti s h- I laim l. A rotary earn-controlled electrical switch comprising, in eombina tion a plurality of axially aligned housing units, each housing unit having two axially spaced end walls with ,axially aligned apertures in the end walls, acam rotatablymounted in each housing unit for actuatingat least oneci-rcuit breakingelement with an actuating force perpendicular to the axis of rotation of the cam, andeach cam comprising two axially extending tubular hubs, one of said hubs carrying a coupling having a serrated periphery while theother hub has acorrespondingly serrated axial bushingengageable by said coupling of an adjacent one. of said cams whereby adjacent cams may be coupled together against relative rotational movement to form a single rotary cam-unit for said switch, said cams consisting of a high-melting,electrically insulating therrno-plastic resin selected from the group consisting of polyarnicles, superpolyamides and resins substantially equivalent theretoin mechanical strength, tenacity, moderate'elasticity and abrasion-resistance, and axially aligned bearings being provided in said housing unit end walls to receive at least one of said hubs of eachcam and to support the cams rotatably in said housing units.

2. The rotary-cam-cont-rolled electrical switch of claim 1, wherein each cam forms an integral element withits cam hubs and their coupling and bushing, respectively, each element having a central bore therethrough.

The rotary cam-controlled electrical switch of claim The multiple In the case of breakdown 1, comprising a switch actuating clement adjacent an end 2,757,250 Brown July 31, 1956 one of said cams, the coupling of said end cam facing the 2,796,474 Glogau June 18, 1957 actuating element and the actuating element gripping the FOREIGN PATENTS periphery of the cam hub carrying said coupling.

103,183 Australia Feb. 2, 1938 References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES 2,262,306 Thompson Nov. 11, 1941 Product Engineering, September 1948, pp. 140 and 2,588,632 Jefirey Mar. 11, 1952 10 141 relied I 

